<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>js0201</title>
</head>
<body>
<script>
    var i = 20;//number
    i = 'ok';
    i = "hello";//string
    i = [];
    i = new Object(); //object
    i = function(){}//function
    i = {};
    i = new Array();//object
    i = null;//null object

    document.write(typeof(a));  //undefined
</script>
<hr>
<script>



</script>
</body>
</html>